Check out Two settings to make using the Mac App Store easier

If you are a frequent shopper at the Mac App Store and are tired of entering your password each time you go to download an app, there are two settings you should know about. Unfortunately, it seems to me you can't use both at the same time.
To find them, open System Preferences, choose App Store and look at the Password Settings area at the bottom.
Change the first setting, Purchases and In-app Purchases, from Always Require to Require After 15 minutes. Now, you can download a bunch of apps within a 15 minute window and enter your password only once.
For the other setting, Free Downloads, change it from Require Password to Save Password. With this setting, you can install free apps without needing to enter your password.

Keep in mind that saving a password for free downloads doesn't mean you'll never be asked for your password again when attempting to download a free app. You'll still be asked for your password unless you have recently installed an app from the App Store and entered your password.
Of course, you may want to think twice about changing either of these settings if you have kids in your house or a roommate who doesn't respect boundaries.
According to OS X Daily, these settings are available only with OS X 10.11 El Capitan.